Rotary stud switches



March 19, 1957 K|RHEL 2,786,104

ROTARY STUD SWITCHES Filed Oct. 23, 1953 my ezz'l'op United States ROTARY STUD SWITCHES Alan Arthur Kirchel, Beckenham, England, assiguor to Muirhead & Co. Limited, Beckenham, England Application October 23, 1953, Serial No. 387,947

Claims priority, application Great Britain November 4, 1952 6 Claims. (Cl. 200-11) This invention relates to rotary stud switches of the kind comprising a series of contact studs, an associated slipring or disc and a sliding connector arranged to move from stud to stud to connect electrically any selected stud on the common slipring.

The invention consists of a switch of the kind described in which the sliding connector is formed from resilient metal sheet.

An object of the invention is to provide an improved type of rotary stud switch having a low value of contact resistance.

A further object is to provide a switch which will maintain this same low value of contact resistance over long periods of time.

An additional object is to provide a switch which will operate indefinitely without additional lubrication.

The connector preferably has its centre part removed. This improves its resilience and also helps to reduce the capacitance which is a feature of the invention.

The resilient connector is preferably held on to the studs and slipring or disc by means of a spring-loaded stirrup-piece bearing on it over the slipring or disc and over the contact studs.

The invention will be further described with reference to the embodiment shown in the accompanying drawings.

Figure 1 is a section through the axle of a rotary stud switch.

Figure 2 is a perspective exploded view of a part thereof on a larger scale.

Figure 3 is a view from the right of Figure l, partly cut away.

Figure 4 is a view from the left of Figure l, partly cut away.

Figures 5 and 6 show details of the two modifications.

Figures 7, 7a, 8, 8a, 8b, 9 and 9a show various alternative forms of stirrup piece.

Referring to the drawings, the main frame of the switch comprises parts 1 and 1a. Contact studs 2 are shown arranged around a common disc 3, both 2 and 3 being provided with silvered surfaces 4 and 4a in order to minimise the effect of oxidation upon the contact resistance of the switch. The connector 5 is made of thin copper sheet and has contact pads 6 attached to it. Contact pads 6 are made preferably of sintered silver material containing a small percentage of graphite, and require no further lubrication. Spring 7 provides the necessary contact pressure and stirrup 8 applies the force of spring 7 to the contact pads 6.

It will be seen that stirrup 8 has three feet 9 which ensures that the stirrup seats itself correctly upon the connector 5 and that the force is applied approximately on the centre-line of the contact pad 6 that is associated with the studs 2. This feature is not so important with regard to the contact pad 6 associated with the common disc 3 since that contact slides on an unbroken surface.

The connector 5 being of thin material and having the centre portion removed as shown, has sufticient resilience to allow the pads 6 to accommodate themselves to the stud and slipring surfaces, yet the cross-section is such that the electrical resistance from contact to contact is sufficiently low for practical purposes.

The connector 5 is located and driven rotationally by a projection or projections 10, passing through the centre portion thereof, which are secured to or are part of rotor arm 11 which in turn is driven by shaft 12 and hand knob 13. Projections 10 also serve to locate the stirrup piece 8 in the correct position relative to connector 5 by engaging in notches'in the sides of the stirrup piece 8.

The shaft 12 can, if=desired, be provided with a detent 14 and; retaining springlS in known manner, so as to retain the switch rot or in any set position.

In a variation shown in Figure 5, the contact assembly 5 and 6 may be drilled or, alternatively, constructed so that a cavity is provided in the contact pad 6 as shown, and the single pressure point 9 of the stirrup 8 presses at the bottom of the cavity. This construction provides a maximum of stability of the contact pad.

In a further variation shown in Figure 6, the connector 5 may be formed with two deep depressions as shown, to which may be attached by suitable means a minimum quantity of the precious metal contact material.

The connector 5 may be made of other material than copper, if desired. In a preferred construction it is made of beryllium copper sheet.

In an alternative construction the connector 5 may be made of silver-phosphor bronze bi-metal sheet with the contact pads 6 attached to the silver side. This arrangement has the advantage of providing the lowest possible resistance path due to the silver, combined with the resilience and strength of the phosphor bronze backing.

In a further alternative construction the connector may be made of two or more laminations.

Referring to the construction of the stirrup piece, while this is shown on the main drawing as having three pressure points it can, as shown in Figures 7-9, alternatively be constructed with appropriate radii, or alternatively have domed pressure points, the radii being such that the stirrup efiectively controls the flatness of the connector in contacting both the studs and the slipring.

In a further alternative the connector could have contacts on it which are not circular in form; they could be square or rectangular and in another alternative the portion of the connector contacting the slipring could be provided with two contacts.

Various modifications may be made within the scope of the invention.

I claim:

1. An electric switch comprising contact studs mounted in circular disposition, a concentric contact ring, said studs and ring having flat contact surfaces, a resilient floating connector to make contact between any selected stud and the contact ring, said connector having attached to it two circular contact pads with flat contact surfaces making contact respectively with the studs and the contact ring, and an independent spring-loaded stirrup having two legs which apply pressure respectively to the two contact pads.

2. A switch as claimed in claim 1, in which one leg of the stirrup applies pressure to one contact pad at two points equally spaced on either side of its centre and the other leg applies pressure to the other contact pad at its centre.

3. A switch as claimed in claim 1 in which the contact pads are of equal diameter and the spring loading of the stirrup is effected by means of a coiled spring which acts at the centre of the stirrup to apply equal pressures to the two contact pads.

4. A switch as claimed in claim 1 characterised in that the contact pads are composed of a sintered mixture of a Patented Mar. 19, 1957- metal having a low electrical resistance such as silver and a dry lubricant such as graphite.

5. A switch as claimed in claim 1 in which the connector has its centre part removed and is arranged so that when one contact pad is in contact with a stud, the other contact padis in contact with that portion of. the contact ring immediately adjacent to the said stud. V

6. A switch as claimed in claim 5 in which the connector and stirrup are located and driven rotationally by a projection or projections passing on either side of the stirrup and through the centre portion of the connector and which are secured to, or are part of, a rotor arm which in turn is driven by a shaft and hand-knob.

References Cited in the file of this patent 1 UNITED STATES PATENTS 703,234 Brown June 24, 1902 

